Based on the observing data of electro-magnetic field and other plasma parameters on DEMETER satellite of France, the anomalous variations in ion temperature Ti, ion density Ni, Very Low Frequency (VLF) magnetic spectral values and so on were analyzed before Yutian 7.2 earthquake in Xinjiang. The analysis on Ti shows that the abrupt abnormal signals above epicentral area occur frequently in a much wider space, so they are with lower reliability as seismic precursors. Using revisited orbit method to compare the shapes of the density of H+, it is found that all curves in a year are with consistent shape, but the peak amplitude in summer and autumn is 1 times of that in spring and winter. Compared the curves of Ni in 2008 with those in 2007 and 2006, apparent increases were exhibited at peak value regions in one month prior to Yutian earthquake with the amplitude rising to more than a magnitude relative to the other two years since February, and it continued to the earthquake occurrence. As for the magnetic spectrum data, orbits were selected in the distance of 2000\,km and single frequency (400 Hz) values were extracted and arranged to a time series according to their record date and common latitude scale (0~60°N). The results show that during 2 days before the earthquake, the spectrum values at 400 Hz increased approximately by an order of magnitude, reflecting an obvious electro-magnetic emission occurred in ionosphere before the earthquake. It is illustrated after processing the three components of ELF electric and magnetic field on March 20 by vector analysis that, some left-rotated polarization electro-magnetic signals existing at the observing period reflect that the variation of ion density in ionosphere was accompanied by the emission of ELF electro-magnetic signals. Summing up, the variation process of these ionospheric parameters is consistent to the coupling mechanism of earthquake preparation and ionosphere at present.